Clinical Pearls & Morning Reports
Published April 18, 2018
Placenta accreta spectrum includes placenta accreta (attachment of the placenta to myometrium without intervening decidua), placenta increta (invasion of the trophoblast into the myometrium), and placenta percreta (invasion through the myometrium, serosa, and into surrounding structures). The problem occurs when the placenta does not detach normally from the uterus after delivery of the fetus, leading to bleeding, which is often severe. Read the latest NEJM Clinical Practice here.
Q: What are some of the risk factors for placenta accreta spectrum?
A: Placenta accreta spectrum may occur after any procedure or manipulation that damages the endometrium, including uterine curettage, myomectomy, endometrial ablation, uterine-artery embolization, or manual removal of the placenta. The most common risk factors are placenta previa (placenta that partially or completely covers the cervical os) and previous cesarean delivery; the risk is greater when both factors are present and when the previa overlies the scar. Other risk factors include an abnormally adherent placenta in a previous pregnancy, advanced maternal age, increasing parity, and in vitro fertilization.
Q: How is placenta accreta spectrum diagnosed?
A: Obstetrical sonography in the second or third trimester of pregnancy is the mainstay of antenatal diagnosis, and abnormalities suggestive of placenta accreta spectrum are well described. Ultrasonography in the second and third trimesters is reported to identify placenta accreta spectrum with sensitivities and specificities of 80 to 90%. These may be overestimates, however, because data are derived from experts aware of the a priori risk on the basis of clinical risk factors.
A: A decision analysis involving women with accreta and placenta previa showed that delivery at 34 weeks of gestation was the preferred strategy for balancing maternal and neonatal risks. In the absence of better information, planned delivery at 34 weeks of gestation is considered appropriate in asymptomatic women in whom clinical and imaging findings strongly suggest placenta accreta spectrum. Most centers only hospitalize women with bleeding or threatened labor, but some admit all women with the condition in the middle of the third trimester. The preferred surgical approach to placenta accreta spectrum remains uncertain, although most studies show improved outcomes with planned cesarean hysterectomy before the onset of labor or bleeding.
A: A major uncertainty relates to “conservative management” of placenta accreta spectrum intended to preserve the uterus for future pregnancy or to avoid surgical complications. The most common procedure is to perform a planned laparotomy and hysterotomy (avoiding the placenta) with delivery of the baby. The umbilical cord is ligated close to the placenta, and the uterine incision is closed, and the uterus is left in situ. It is expected that the placenta will reabsorb over time. In many cases, pelvic devascularization with embolization is used after cesarean delivery. Although methotrexate has been used in conservative management, its use is not recommended, given the lack of evidence of efficacy and the potential risks (including a maternal death attributed to its use). Partial resection of areas of “focal” placenta accreta or the entire lower uterine segment with hemostatic closure of the myometrial defect has also been proposed. However, it is challenging to predict focal accreta with accuracy, data are insufficient to inform efficacy, and the chance of subsequent pregnancy is low.